The incidence of fungal keratitis in Zagazig University Hospitals, Egypt and the value of direct microscopy and PCR technique in rapid diagnosis

Abstract

Objective: To determine the frequency and risk factors of fungal keratitis (FK) and the value of direct microscopy and PCR techniques of corneal smears as appropriate diagnostic methods. Methods: The keratitis cases in Ophthalmology Department of Zagazig University Hospitals, between January and June 2012 were enrolled. Corneal samples were examined by direct microscopic examination of wet mount preparation with KOH (10%), PCR technique and cultured simultaneously. The corneal smear and PCR findings were compared to the culture results to analyze specificity, sensitivity and predictive values of these techniques. Results: A total of 350 patients diagnosed as keratitis and 60 of them were included in the study by a systemic random sampling method. The FK was proven in 33 (55%) cases with culture results. Ocular trauma (63.6%) was the most prevalent predisposing factor. The cultures revealed that the most frequent fungal pathogen were Penicillium spp. (24.2%) followed by Aspergillus fumigatus (21.2%). Direct microscopic examination had a sensitivity of 100%, specificity of 66.7%, a positive predictive value (PPV) of 78.6% and a negative predictive value (NPV) of 100%. PCR had a sensitivity of 100%, specificity of 88.9%, a PPV of 91.7% and a NPV of 100%. Conclusion: Although, PCR is able to detect fungi in a high proportion of culture negative cases, it is difficult to be used as a routine diagnostic test due to the economic reasons. Therefore, we strongly recommend the use of direct microscopy of corneal smear as a rapid, economic and sensitive method for screening of FK.

Utility of polymerase chain reaction for rapid diagnosis of pediatric fungal keratitis : A comparative study with conventional mycological work up

“…Herein, trauma as the mostly prevalent predisposing element representing 57% cases followed by vernal keratoconjunctivitis (20%) which is a common allergic problem in our community with a noticeable seasonal variation. In a preceding study done by El Shabrawy et al on diverse age groups of patients with fungal keratitis [16] they stated that trauma (63.6.%) followed by chronic liver disease (30%) were the most common predisposing factors.…”

“…Cycling conditions were set as follows: initial denaturation (95 °C, 10 min), then 49 denaturation cycles (95 °C, 1 min), annealing (50 °C, 1 min), followed by extension (72 °C, 2 min) and a final extension phase (72 °C, 10 min). Each PCR run comprised a positive control having purified Aspergillus fumigatus DNA in addition to two negative controls having blank reagents [16].…”

“…Separation of amplification products was conducted by means of electrophoresis using agarose gel (1%), followed by staining by means of ethidium bromide, in addition to analysis utilizing a gel electrophoresis. Interpretation of PCR products (260 bp length) was described as positive result, indicating the existence of fungal element [16].…”

Evaluation of impression cytology as rapid non-invasive diagnostic tool in infected corneal ulcer

“…According to Bharathi et al (2006) , a smear is a reliable test for initiating specific medical treatment until culture results confirm the diagnosis. Also, Shabrawy et al (2013) strongly recommend the use of direct microscopy of a corneal smear as a rapid, economic, and sensitive method for screening for fungal keratitis. But Shemis and Rahman (2012) , Fanselow et al (2021) , and others concluded that direct smear and culture techniques are of great diagnostic value for the management of MK.…”

“…(Alkatan et al, 2019, Goh et al, 2018. Many studies consider smear and culture as the basic standard diagnostic methods for MK (Tananuvat et al, 2012, Shabrawy et al, 2013. Another important benefit of the culture is testing for antibiotic sensitivity, but we cannot wait for its results to start the medical treatment; corneal perforation in fungal keratitis can occur in a few days, and culture results take days to appear; also, corneal melting in acanthamoebic keratitis and Pseudomonas keratitis occurs very rapidly [Rai et al, 2016, Bharathi et al, 2006, Kaye et al, 2016.…”